1. Field of the Invention
The invention relates to a method of manufacturing a shift gearwheel with coaxially disposed and axially projecting shift teeth, which have an axial undercut.
2. Description of the Related Art
Shift gearwheels of the type indicated above are used, for example, in synchromesh transmissions for motor vehicles. For general appreciation, a cutout of a synchronizing unit belonging to prior art is first described with reference to FIGS. 1 and 2a-c.
FIG. 1 shows an exploded view of a loose wheel 1 with clutch body 7, a synchronizing ring 2, a sliding sleeve 3 and a synchronizer body 4.
The loose wheel 1 is provided with an external gearing 20. Integrally formed on its end face is a clutch body 7. The clutch body 7 comprises a coaxial ring of shift teeth 5, which--starting from a coaxial groove 6 forming an undercut--extend in axial direction to the left and project beyond the end face of the loose wheel 1. The shift teeth 5 have an axial undercut, such that the width of said shift teeth 5--starting from the tooth tip--diminishes towards the base of the groove 6. The shift teeth 5 at their tip end have a roof slope, which terminates at an annular surface 14 extending at right angles to the axis. Raised up from said annular surface 14 is a coaxial friction cone 8.
The synchronizing ring 2 at its outside is provided with a ring of shift teeth 9, which extend in axial direction between two annular surfaces 10 and 11 extending at right angles to the axis. The inner surface of the synchronizing ring 2 matches the friction cone 8 on the clutch body 7.
The sliding sleeve 3 is provided with axially extending shift teeth 12 and arranged so as to be axially displaceable but non-rotatable on the synchronizer body 4. To said end, the synchronizer body 4 in turn has axially extending teeth 13, which mesh with the inner shift teeth 12 of the sliding sleeve 3. The shift teeth 12 of the sliding sleeve likewise have an undercut close to their two axial ends.
FIG. 2 shows the positions of the shift teeth of the transmission elements shown in FIG. 1 in three different shift positions, and indeed as a developed sectional view.
FIG. 2a shows the neutral position of the synchronizing shift device. Here, the sliding sleeve 3 is in centre position. The loose wheel 1 with its clutch body and a further loose wheel (not shown) is freely rotatable relative to the synchronizer body. The shift teeth 12 of the sliding sleeve 3, the shift teeth 9 of the synchronizing ring 2 and the shift teeth of the clutch body have clearance relative to one another.
FIG. 2b shows the transmission elements in blocking position. The sliding sleeve 3 and the synchronizing ring 2 have been displaced to the right. The synchronizing ring 2 therefore comes into frictional engagement with the friction cone 8 of the clutch body 7 and is rotated so that the shift teeth 12 of the sliding sleeve and the shift teeth 9 of the synchronizing ring 2 lie with their roof slopes against one another.
FIG. 2c shows the "gear engaged" position. Here, the sliding sleeve has been slid so far to the right that the shift teeth 12 of the sliding sleeve 3 engage fully through the shift teeth 9 of the synchronizing ring 2 and moreover project into the shift teeth 5 of the clutch body 7. It may be seen that the undercuts of the shift teeth 12 of the sliding sleeve 3 upon transmission of a torque and the undercuts of the shift teeth 5 of the clutch body 7 engage one behind the other, thereby preventing an axial separation of the transmission elements. This is the purpose of the undercuts.
A plurality of methods of manufacturing shift gearwheels with undercut shift teeth are already known.
Thus, the prior publication DE 20 40 413 A describes a known method whereby tapered gearwheels with undercut teeth may be manufactured in that teeth with parallel extending tooth flanks are first manufactured by rough-pressing and then finish-edged so as to form a roof shape.
A method of manufacturing a synchronizing component provided with an abridged gearing with undercut teeth for shift transmissions is further known (DE 34 27 156 C2), in which rough-forging is used first to manufacture a semifinished product, the abridged gearing of which comprises teeth having an overmeasure exceeding the height of the finished tooth tip. Then, by means of a plurality of sizing impacts the cold semifinished product is worked in such a way that first the tooth tips are rough-edged, during which the teeth are supported at their radially outer sides against the forging die. At the same time, by means of the rough-edging or a further sizing impact a strain-hardening is produced in each case in the tooth region of the teeth. Then the tooth tips are finish-edged so that they have a roof shape and the tooth flanks have the inclination corresponding to their undercut.
Finally, a method of machining clutch gearwheels for motor vehicle transmissions is additionally known (DE 34 38 454 A1), whereby in a first working step a blank of a round rod is formed by cold- or hot-forging from a material which is deformable under pressure. In a second working step, the blank is pressed by means of a forging die. In said manner, the cross section having the defined final dimensions and at the same time a taper-face projection are obtained. In a third working step the taper-face projection is converted into a tooth shape. In a fourth working step the tooth shape is pressed into the forging die from an end face of the opposite end of the taper-face projection so that the tooth shape is provided with an undercut.
An object of the invention is to indicate a non-cutting method of manufacturing a shift gearwheel having axially undercut shift teeth, which is particularly easy to effect and suitable for mass production.
According to one aspect of the invention, there is provided a novel method of manufacturing a shift gearwheel with coaxially disposed and axially projecting shift teeth and which have an axial undercut. This method includes a first step of bringing into mutual engagement, a shift gearwheel blank having coaxially disposed and axially projecting preformed shift teeth, and a forming tool having corresponding axial tooth recesses, such that the preformed gearweel blank shift teeth become engages in the forming tool tooth recesses with a clearance; a second step of setting the shift gearwheel blank and the forming tool in gyratory motion relative to one another in such a way that the contours of the tooth recesses move in a pressing and material-shaping manner over the flanks of the performed gear wheel shift teeth so as to form an undercut; and a third step of separating the thus machined shift gearwheel blank and the forming tool from one another.
The method according to the invention is particularly notable for the fact that it may be effected continuously throughout without interruption of the individual teeth and leads to reproducible products. The method is simple as well as time- and cost-saving.
Advantageous refinements of the method according to this aspect of the invention are described hereinafter.
The invention in another aspect relates to a device, with which the previously described method may be effected. According to a further refinement, the shift gearwheel blank is maintained stationary and the forming tool is made to simultaneously execute a rotation about an axis of nutation, a nutating movement about a vertical axis of rotation and a lifting movement in the axial direction.
According to a still further refinement, the shift gearwheel is caused to execute a lifting movement in the axial direction while the forming tool simultaneously executes a nutating movement.
In yet another refinement, the invention relates to a shift gearwheel manufactured by the above described method.
An additional refinement involves successively increasing the angle of nutation between the shift gearwheel blank and the forming tool from 0.degree. up to a maximum angle of nutation, maintaining the angle at the maximum angle of nutation and then reducing the angle back down to 0.degree..
Yet another refinement involves carrying out the gyratory motion first in one direction of nutating movement and then repeating the gyratory motion in the opposite direction of nutating movement.